The High Cycle and Speed (HCS) valve is a pneumatically operated diaphragm valve for the Ultra High Purity (UHP) market. UHP valves are used, for example, in the manufacture of semiconductors in a process known as Atomic Layer Deposition (ALD). The gases used in ALD processes need to be free of impurities, which would compromise the function of the resultant semiconductors. ALD valves are required to open and close rapidly with a closing force of around 70 pounds of pressure. Pneumatic actuators generally are used to operate these valves because a pneumatic actuator can provide the requisite large closing force in a compact package, while being free of the kind of flammability risks associated with electronic solenoid-operated valves. ALD valves are required to perform many actuation cycles in a short period of time, typically having a response time below 20 milliseconds. Such rapid response time and related high cycling renders manual valves impractical, and pneumatically actuated valves are therefore preferred.
One measure of valve life, and thus valve reliability, is referred to in the art as the Mean Time To Failure (MTTF). MTTF typically is denoted as the number of cycles to valve failure. Conventional HCS valves have achieved MTTF measures on the order of one million cycles. Given the high cycling of HCS valves, however, such as in ALD processes, even a one million cycle MTTF significantly constrains the useful life of such valves. The need for frequent valve replacement or repair remains a substantial performance issue for HCS valves, particularly in ALD and comparable processes.
One source of potential HCS valve failure is valve seat wear. When the valve is in the closed position, the portion of the valve seat that contacts the diaphragm compresses slightly under the force of the diaphragm when the valve is closed to provide an effective sealing surface. Otherwise, the valve seat is substantially rigid and generally considered non-moving in a gross sense. It is known, however, that in actuality there indeed tends to be slight movement and displacement of the valve seat relative to the adjacent valve components that house the valve seat. In particular, high gas pressure from the inlet side of the valve tends to move the valve seat out of position. For example, in conventional HCS valves for ALD processes, valve seat movement tends to be on the order of 0.001 inches per cycle. Such repeated displacement is sufficient to damage the valve over time, for as the valve seat moves against adjacent valve components, the friction causes valve seat wear to occur. The valve seat wear results in leakage space being present even when the valve is closed, which permits external leakage of the fluids flowing through the valve. With the high cycling of HCS valves, even the slight movement of the valve seat accumulates significant valve seat wear that diminishes the valve life.
Another source of potential HCS valve failure is fatigue failure of the diaphragm that results in the valve being unable to close fully. This also can result is external leakage of the fluids flowing through the valve. Many HCS valve components, including the diaphragm and associated cap against which the diaphragm presses, are made of rigid metal materials such as, for example, stainless steel. The rubbing of the metal diaphragm against adjacent metal components (e.g., against the valve cap or again another stainless steel diaphragm in a multi-diaphragm configuration) leads to damaging wear of the diaphragm. This type of wear caused by the rubbing of adjacent metal surfaces commonly is referred to in the art as “fretting”. The fretting also may occur unevenly across the diaphragm, and where the fretting is concentrated cracks can occur in the diaphragm.
In view of both valve seat wear and diaphragm fretting, the reliability and valve life, as measured for example by the MTTF, has proven to be deficient for high cycling applications.